Method and Apparatus for Forward Error Correction

1. A multi-tone transceiver with a plurality of components forming a transmit path and a receive path configured to couple via a subscriber line to an opposing multi-tone transceiver for frequency division multiplexed multi-tone modulated communications therewith; and the multi-tone transceiver comprising: a hybrid front end that couples the receive path to the subscriber line; a noise margin channel identifier component on the receive path configured to identify within a received tone set, discrete tones each associated with a corresponding one of at least two channels differing from one another in a relative noise margin of associated tones; and a Viterbi decoder component on the receive path coupled to the noise margin identifier component and responsive to the tone identification provided by the noise margin channel identifier component to discretely decode each of the corresponding at least two channels; thereby improving the fidelity of the error correction provided by the Viterbi decoder by discretely processing the identified tones within the received set of tones.

2. The multi-tone transceiver of claim 1 wherein the Viterbi decoder component further comprises: a scaler sub-component for determining a discrete scale factor associated with each of the at least two channels identified by the noise margin identifier, and the scale factor for each channel based on an associated noise margin of the associated tones of the channel; and a branch metric sub-component responsive to the scale factor for each channel determined by the scaler sub-component to scale a branch metric for the discrete tones associated with each channel accordingly.

3. The multi-tone transceiver of claim 1 wherein the Viterbi decoder component further comprises: a branch metric sub-component to determine a branch metric between each possible state associated with successive discrete tones within the received tone set; a path metric sub-component coupled to the branch metric sub-component to determine an optimal incoming path for each state; a trace back sub-component to derive an optimal path back through the states processed by the path metric sub-component; and a trellis termination controller sub-component responsive to the identification provided by the noise margin identifier of discrete tones within the received tone set associated with each of the at least two channels, to configure the branch and path metric sub-components together with the trace back subcomponent to discretely decode each of the at least two sub-channels; thereby avoiding overlap in decoding of the at least two channels.

4. The multi-tone transceiver of claim 1 having the noise margin channel identifier further configured to identify the at least two channels by calculating noise margins of the received tone set based on per tone bit loading and per tone signal to noise ratios.

5. The multi-tone transceiver of claim 1 further comprising: a trellis encoder component on the transmit path to trellis encode in each successive symbol interval transmitted data from at least two channels differing from one another in a relative noise margin for associated tones and to terminate the trellis in an identifiable state at a tone boundary between the at least two channels, whereby at least one intermediate termination is introduced into the trellis in each symbol interval.

6. The multi-tone transceiver of claim 1 wherein the Viterbi decoder component further comprises: a metric calculator sub-component configured to determine a branch metric for a received set of tones; a scaler sub-component for determining a discrete scale factor for each tone among the received set of tones based on an associated noise margin of the associated channel; and a binary left/right shift register having a control input coupled to the scaler sub-component, an input coupled to the metric calculator sub-component and an output, and the binary left/right shift register scaling the branch metrics for the received set of tones determined by the metric calculator sub-component in binary increments determined by the discrete scale factors determined by the scaler sub-component by effecting a corresponding left or right shift of the branch metrics for the received set of tones determined by the metric calculator.

7. The multi-tone transceiver of claim 1 wherein the Viterbi decoder component further comprises: a branch metric sub-component to determine a branch metric between each possible state associated with successive discrete tones within the received tone set; a path metric sub-component coupled to the branch metric sub-component to determine an optimal incoming path for each state; a trace back sub-component to derive an optimal path back through the states processed by the path metric sub-component; a windower sub-component coupled to the branch, path, and trace back subcomponents for configuring same to decode the received tone set in windowed increments having a length less than the length of the tones associated with a channel; and a trellis termination controller sub-component coupled to the windower subcomponent and responsive to the identification provided by the noise margin identifier of discrete tones within the received tone set associated with each of the at least two channels, to configure the windower sub-component to discretely decode each of the at least two sub-channels including adjustment of the windowed increments to avoid overlap in decoding of the at least two channels.

8. A multi-tone transceiver with a plurality of components forming a transmit path and a receive path configured to couple via a subscriber line to an opposing multi-tone transceiver for frequency division multiplexed multi-tone modulated communications therewith; and the multi-tone transceiver comprising: a hybrid front end that couples the transmit path to the subscriber line; a trellis encoder component on the transmit path to trellis encode in each successive symbol interval transmitted data from at least two channels; and a trellis terminator component coupled to the trellis encoder component configured to terminate the trellis in an identifiable state at a tone boundary between the at least two channels, whereby at least one intermediate termination is introduced into the trellis in each symbol interval.

9. A method for frequency division multiplexed multi-tone modulated communications on a multi-tone transceiver configured to couple to a subscriber line; and the method comprising: identifying within a received tone set, discrete tones each associated with a corresponding one of at least two trellis encoded channels differing from one another in a relative noise margin of associated tones; and discretely decoding each of the at least two tones identified in the identifying act, thereby improving the fidelity of the error correction provided by the corresponding trellis encoded channels by discretely processing the identified tones within the received set of tones.

10. The method of claim 9 , wherein the decoding act further comprises: determining for each of the at least two trellis encoded channels corresponding to the tones identified in the identifying act, a discrete scale factor for each channel based on an associated noise margin of the associated tones of the channel; and scaling a branch metric for the discrete tones associated with each channel based on the scale factor determined in the determining act.

11. The method of claim 9 , wherein the decoding act further comprises: determining a branch metric between each possible state associated with successive discrete tones within the received tone set; determining an optimal incoming path for each state determined in the first determining act; deriving an optimal trace back path through the states processed in the second determining act; and discretely executing the first and second determining acts and the deriving acts to discretely decode each of the at least two sub-channels; thereby avoiding overlap in decoding of the at least two channels.

12. The method of claim 9 , wherein the identifying act further comprises: calculating noise margins of the received tone set based on per tone bit loading and per tone signal to noise ratios.

13. The method of claim 9 , further comprises: trellis encoding in each successive symbol interval transmitted data from at least two channels differing from one another in a relative noise margin for associated tones; and terminating the trellis in an identifiable state at a tone boundary between the at least two channels.

14. The method of claim 9 , wherein the decoding act further comprises: determining a branch metric for a received set of tones; determining a discrete scale factor for each tone among the received set of tones based on an associated noise margin of the associated channel; and scaling the branch metrics determined for the received set of tones in the first determining act in binary increments in correspondence with the discrete scale factors determined in the second determining act by effecting a corresponding left or right shift of the branch metrics determined for the received set of tones in the first determining act.

15. The method of claim 9 , wherein the decoding act further comprises: determining a branch metric between each possible state associated with successive discrete tones within the received tone set; determining an optimal incoming path for each state determined in the first determining act; deriving an optimal trace back path through the states processed in the second determining act; discretely executing the first and second determining acts and the deriving acts in windowed increments having a length less than the length of the tones associated with a channel; and adjusting the windowed increments to avoid overlap in decoding of the at least two channels.

16. An apparatus for frequency division multiplexed multi-tone modulated communications on a multi-tone transceiver configured to couple to a subscriber line; and the apparatus comprising: means for identifying within a received tone set, discrete tones each associated with a corresponding one of at least two trellis encoded channels differing from one another in a relative noise margin of associated tones; and means for discretely decoding each of the at least two channels identified by the identifying means, thereby improving the fidelity of the error correction provided by the trellis encoded channels by discretely processing the identified channels within the received set of tones.

17. The apparatus of claim 16 , wherein the means for discretely decoding further comprises: means for determining for each of the at least two trellis encoded channels corresponding to the tones identified by the identifying means, a discrete scale factor for each channel based on an associated noise margin of the associated tones of the channel; and means for scaling a branch metric for the discrete tones associated with each channel based on the scale factor determined by the determining means.

18. The apparatus of claim 16 , wherein the decoding means further comprises: means for determining a branch metric between each possible state associated with successive discrete tones within the received tone set; means for determining an optimal incoming path for each state determined in the first determining means; means for deriving an optimal trace back path through the states processed by the second determining means; and means for discretely controlling execution of the first and second determining means and the deriving means to discretely decode each of the at least two sub-channels; thereby avoiding overlap in decoding of the at least two channels.

19. The apparatus of claim 16 , wherein the identifying means further comprises: means for calculating noise margins of the received tone set based on per tone bit loading and per tone signal to noise ratios.

20. The apparatus of claim 16 , further comprises: means for trellis encoding in each successive symbol interval transmitted data from at least two channels differing from one another in a relative noise margin for associated tones; and means for terminating the trellis in an identifiable state at a tone boundary between the at least two channels.

21. The apparatus of claim 16 , wherein the decoding means further comprises: means for determining a branch metric for a received set of tones; means for determining a discrete scale factor for each tone among the received set of tones based on an associated noise margin of the associated channel; and means for scaling the branch metrics determined for the received set of tones by the first determining means in binary increments in correspondence with the discrete scale factors determined by the second determining means by effecting a corresponding left or right shift of the branch metrics determined for the received set of tones by the first determining means.

22. The apparatus of claim 16 , wherein the decoding means further comprises: means for determining a branch metric between each possible state associated with successive discrete tones within the received tone set; means for determining an optimal incoming path for each state determined by the first determining means; means for deriving an optimal trace back path through the states processed by the second determining means; means for controlling execution of the first and second determining means and the deriving means in windowed increments having a length less than the length of the tones associated with a channel; and means for adjusting the windowed increments to avoid overlap in decoding of the at least two channels.